ToF-SIMS

Description

Time-of-Flight Secondary Ion Mass Spectrometry

ToF-SIMS uses a focused, energetic primary ion beam to bombard the surface of the sample of interest. Sample atoms are sputtered and those that are ionized (secondary ions) are accelerated towards a mass spectrometer where they are mass separated before being detected. Either positive or negative secondary ions are detected. The use of a reactive primary ion beam can increase the secondary ion yield. Oxygen is used to increase positive secondary ion yield and cesium is used to increase negative secondary ion yield. ToF-SIMS can provide surface mass spectra, images with lateral resolution in the 0.1 to 10µm range and depth profiles with depth resolution in the 1 to 10nm range. SIMS can be quantitative when reference samples are used and can achieve ppm or even ppb sensitivity. Profile depths can range from a few tens of nanometers to several tens of microns and any vacuum compatible sample can be analyzed. Some samples may require specific sample preparation (notably for biological samples) and analysis conditions. For example organic samples may be damaged by mono-atomic ion beams and the use of cluster ion beams (such as Argon clusters) can reduce this damage, thus enabling large molecular ions, characteristic of the sample to be detected.

A second Ga⁺ ion beam can be used (or FIB) to mill away material to produce a cross section of the sample that can be imaged by ToF-SIMS. Repeating this process several times enables 3-D imaging of micron sized objects to be performed. The in-situ nature of this analysis is especially important for air-sensitive materials and samples that are very heterogeneous with deeply buried features.

One of the instruments is equipped with a Tandem mass spectrometer. This allows easier identification of peaks in the first mass spectra by allowing high mass peaks to be fragmented and reanalysed in a second spectrometer.

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Keywords
Compositional characterization, depth profiling, depth resolution, Imaging mass spectrometry, FIB-TOF-SIMS, 3D analysis

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Specifications

• Available sputter ion sources: Cs⁺, O₂⁺, Ar⁺, Xe⁺, Ar_n⁺ (500<n<5000)
• Impact energy range: from 250eV to 2keV (Cs, O, Xe) Ar up to 5 keV, Ar cluster from 2.5keV to 20keV
• In-situ Ga⁺ FIB gun
• 30kV Bismuth Analysis gun
• Electron gun for charge compensation
• Sample heating (+600°C) and cooling (liquid N₂)
• Depth resolution: ≥1nm
• Mass resolution up to 10,000 m/Δm
• Sample size: typically 1×1cm² but up to ∅100mm diameter
• Analysed area: crater between 50µm to 500µm for Depth profiling. Imaging up to 5mm²
• ION ToF 5 and NanoToF II instruments available with possibility to transfer samples in UHV or N₂ environment to AFM, XPS, XPEEM and NanoAuger instruments at the CEA-Leti
• The analysis is destructive

Ascent+ facility
CEA-Leti

Platform Technologies

• Nano for Quantum Technologies
• Disruptive Devices
• Advanced Integration

Key Enabling Capability

• Metrology / Characterisation: Physical

Typical Applications
Previous access requests have involved:

1. Imaging of Al nanoparticles in a metal matrix to compare with other imaging techniques
2. Searching for organic or metallic contamination at interfaces
3. Evaluation of diffusion in multilayer stacks

Publications
[DOI: 10.1016/j.orgel.2018.04.031]
[DOI: 10.1021/acs.analchem.9b02545]
[DOI: 10.1021/acs.analchem.7b00279]
[DOI: 10.1017/S1431927616012502]